1. Field of the Invention
This invention relates to constant quantity injection valves for liquefied carbon dioxide gas and also to injectors and injection apparatus using such valves.
2. Description of the Prior Art
Quantitative injection apparatuses used in connection with asthma or the like use furon as propellant. Furon is under comparatively low pressure. Packing materials such as rubber have low permeability to furon, and it is not so difficult to maintain seal against furon.
(Problems to be Solved According to the Invention)
Furon is raising problems such as destruction of ozone layer, and its use will be prohibited in the future. When realizing the adoption of liquefied carbon dioxide gas as a substitute propellant, it is important that the pressure of the gas is very high compared to furon, that is, the gas pressure is about 60 to 70 kgf/cm2 even at normal temperature.
Therefore, the following problems are posed.
(1) Restriction is imposed on the structure of the valve pins of the first and second valves.
In case of first and second constant quantity valves interlocked to each other for leading gas into and out of a measuring chamber, particularly in case of valves having ring-like packings and valve pins cooperating with one another, the valve pins being moved to repeat the closing and opening of a gas passage, if it is intended to form the valve pins with local notches and transversal holes for the gas passage, stress concentration is caused in ring-like packing portions in contact with the notches, transversal holes, etc. to result in breakage, that is, such processing is impossible.
(2) The packing material such as rubber is highly permeable to the gas, and volume expansion, i.e., inflation, of the ring-like packings is prone.
As the inflation of the ring-like packings proceeds, the pushing forces of the valve pins are increased to increase the frictional forces with respect to the ring-like packings. The ring-like packings are thus worn out soon. When the inflation proceeds to such an extent that the volume of the ring-like packings exceeds the volume of the accommodating unit, the pushing forces for inserting the closing sections of the valve pins into the ring-like packings are extremely increased, thus making the use difficult or impossible. If it is intended to insert irrationally, damage to the ring-like packings is prone.
To solve the above problems, the structure of the valves and the hardness of the ring-like packing materials are taken into considerations, and it is an object of the invention to provide a constant quantity injection valve which permits use of liquefied carbon dioxide gas and also provide an injector and an injecting apparatus using such a valve.